The mechanism of ferrous ion transport and metabolism by strict anaerobes and facultative anerobic bacteria will be studied. An unusual iron binding protein that we have isolated from Desulforibrio desulfuricans will be studied in detail. By using a variety of physical and chemical techniques, we will try to determine the nature of the iron binding center, which is unique among all non-heme iron proteins in resisting dissociation of the iron even in dilute mineral acid. The mechanism by which this organism solubilizes iron from this resistant protein will be investigated with particular regard to the possible occurrence of low molecular weight ferrous chelating agents. In addition, we will continue our studies on the mechanism of transport of iron in fungi and bacteria. We will gather data to show that ligand exchange, either spontaneous or enzyme catalyzed, is necessary for the acqusition of iron by many organisms. Ferrous ion transport and ligand exchange may both be important in the absorption of iron from animal intestines.